Therefor the skill is simply wrong. You don't survive becuase you learn how to take hits but how not to get hit at all.
Not necessarily . . . take the use of a shield for instance . . . the usage of such isn't based around not getting hit at all. It's about making sure you do get hit, but in the shield, not in your own squishy bits. And it's the same with body armour - learning the defensive advantages of letting yourself be hit, knowing that your armour will absorb the blow, meaning you don't have to put so much effort into complete avoidance, which means more effort into offense.
You survive because you learn how to not get hit at all. As others have implied, part of this, then, is knowing how to move in heavier armours, and more importantly now _not_ to move. If you're wearing a heavy helm with a strong nose-guard, any defensive manoeuvre that will need you to be away of what's 'above' you is a bad idea, because you won't be able to see it due to your helm. Take the battle of the Somme as another example - those in heavy plate who knew to make sure not to fall to ground may have survived. Those that didn't, that may have gone to one leg during an attack/defensive stance, would have never stood up again due to the vacuuming effect of the mud at the time, making for a somewhat easy target, armour or no.
And lastly and by no means leastly, armour only really works well if it is taken care of well. Rusty chain doesn't move with your body, exposing gaps. Un-oiled leather cracks, making holes. Part of an armour proficiency, then, is knowing how to care for your armour so as to maximise its use. It could also be due to gaining knowledge how to better wear it relative to your own sword-style - if you fight right-handed, opening up your right hand side as you fight, you might learn to tighten the buckles on that side, heightening your lateral defence. This would then expose you left side a little . . . but if the way you fight is such that that side is never exposed, it doesn't matter.
Regardless of my yabbering on, I'm sure you'll agree that there are enough _possibilities_ for armour use to have a scaled proficiency system. It may not be perfectly realistic . . . but given this is a pre-alpha test game, we're here to test things, such as systems such as these. Which is what matters.
